NameServers aren't pointed from the dashboard. Your registrar has to point them. Whoever you registered your domain with is where you need to go to point your NameServers back to wordpress.com's NameServers.

Also, if you have custom plugins and such on your site with BlueHost, it's quite likely that those things will not work on your wordpress.com site.

As before mentioned, if you need help with getting your site pointed to wordpress.com, you can contact them for assistance with that.

If you registered your domain through wordpress.com, then you will log into your account there and use them to point the NameServers. It is not something you would do from BlueHost, nor your site on BlueHost.